Field of the Invention
This invention encompasses compositions for providing lubricants and functional fluids with improved frictional properties. Vibrations (shudder or stick slip) in automatic transmissions (AT) caused by continuous slip torque converter clutches and shifting clutches are greatly reduced or eliminated by the use of the fluids of this invention in said transmissions.
Automatic transmission fluids (ATF) are well known in the art. In general however, automatic transmission suppliers and manufacturers specify performance characteristics of the transmission operating with a fluid rather than fluid composition for use in the transmission. It is then up to fluid providers to formulate fluids which meet performance characteristics. Recently, performance requirements for ATFs Service Fills have become more stringent with publication of DEXTRON-III ATF Specification by General Motors, GM 6297M, April, 1993. The Specification is available from General Motors, Material Engineering Transmissions, M/C 748 Ypsilanti, Mich 48197 and is herein incorporated by reference.
Low frequency vibration in continuous slip torque converter clutches (CSTCC) has been defined as shudder. The shudder vibration is related to stick slip friction characteristics of the engaged CSTCC rotating at slow speeds. Further, shudder has two components, initial shudder and shudder durability. The latter is shudder which develops over time. Compositions of the present invention were tested for anti-shudder properties when compared to commercial ATF formulations both for initial shudder and shudder durability. It was found that compositions of this invention eliminated or greatly reduced shudder and shudder durability problems whereas no commercial ATF available performed as well.
Compositions of the instant invention and commercial ATF's were tested in a Chrysler.RTM. minivan with a 41TE transmission. The compositions of the instant invention were by far superior to commercial ATF's in anti-shudder and anti-shudder durability tests. Detailed descriptions of anti-shudder testing procedures are given in SAE TECHNICAL PAPER SERIES NO. 941883, Friction and Stick-Slip Durability Testing of ATF by Ward et al, presented at SAE International Fuels and Lubricants Meeting and Exposition, Baltimore, Md., Oct. 17-20, 1994. This publication is available from SAE International, 400 Commonwealth Drive, Warrendale, Pa. 15096-0001 U.S.A.
In general, automatic transmission fluids comprise a base oil and additives. The base oil may be from natural sources; mineral and plant oils, and from synthetics and will be of the proper viscosity for their intended use. Additives are then incorporated into the base oil with those incorporated being dependent upon the properties that the fluid formulator is striving for. Additives generally can be roughly broken into two groups, chemically inert and chemically active additives as listed below:
______________________________________ Chemically Active Additives Chemically Inactive Additives ______________________________________ anti-oxidants viscosity improvers corrosion inhibitors friction modifiers rust inhibitors defoamers anti-wear agents pour point depressants dispersants detergents seal swell agents ______________________________________
Formulations for ATF's and functional fluids containing some or all of the above additives in a select base oil are freely available in the patent literature. For instance, U.S. Pat. No. 4,209,587 to Koch lists lubricating/functional fluid compositions with various combinations of base oils and additives. U.S. Pat. No. 5,344,579 to Ohtani and Harley describes a friction modifier system for AT and cites additive components for ATF's and their typical ranges. The disclosure of both U.S. patents cited above are herein incorporated by reference. It must be noted that the lines between chemically active and inactive additives are not so distinct. Also, additives may well be multifunctional and are categorized above only for the sake of convenience.